From the Rolls-Royce experimental archive: a quarter of a million communications from Rolls-Royce, 1906 to 1960's. Documents from the Sir Henry Royce Memorial Foundation (SHRMF).
Specifications and design of 'Myth' cam forms, PL.534 and PL.535.
| Identifier | ExFiles\Box 110\1\ scan0070 | |
| Date | 22th April 1941 | |
| 1080 707 To Rm.{William Robotham - Chief Engineer} from Ev{Ivan Evernden - coachwork}/JD.{J. Draper - Frames} c. to Ev.{Ivan Evernden - coachwork} c. to Rm{William Robotham - Chief Engineer}/HH. c. to Rm{William Robotham - Chief Engineer}/OTS. Ev{Ivan Evernden - coachwork}/JD.{J. Draper - Frames}1/SW.22.4.41. Myth Cam Forms. We attach to Rm{William Robotham - Chief Engineer}/HH's copy the originals of the Myth cam forms, PL.534 and PL.535. PL.534 shows an inlet cam of 192 1/2° duration at .030" tappet clearance, and .237" lift. The latter gives an inlet valve lift of .237 x 1.3 = .308". This is a .007" reduction on the valve lift called for in PL.329. It has been dictated by the very short duration and a desire not to reduce the nose radius below .075" on a camshaft which might be made in "Monicrom". In this material, we should prefer not to go below .100" for the nose radius, and we consider that the inlet cam we have designed, is very near the limit in regard to pointedness. PL.535 shows an exhaust cam of 214 1/2° duration at .030" tappet clearance, and .288" lift. Both cams are designed with a section at constant heavy acceleration, followed by an involute and a nose which is purely circular. All toes except the inlet opening toe, are identical with those on B.60 cams. The inlet opening toe has the same gradient as the exhaust opening toe. In the case of B.60 this gradient is reduced through the rocker ratio, i.e., the toes appear the same on the valve lift diagram. This modification has enabled us to shorten the duration by about 2° for the same lift. We wish to instruct two camshafts one having 111 1/2° and another 114 1/2° between the cams. 111 1/2° gives 20° negative overlap at .030" clearance. Owing to the different values of heavy (continued) | ||